The invention relates to a method of transferring a non-PCM encoded audio bitstream read from a digital medium, subsequent to parsing thereof, via an IEC 958 protocolled interface to a multi-channel audio reproduction apparatus.
Digital video disc standardizing is proceeding at an accelerated pace. Commercially available MPEG1 decoder circuit SAA2502 is able to decode compressed digital audio received as a continuous bit stream. Present-day MPEG2 technology has standardized 5 channels, to wit: Left, Right, Center, Left Surround, Right Surround, and furthermore a low frequency enhancement (LFE) channel. The MPEG2 bit stream is distributed into frames of 1152 samples for each of the actual channels, and player operation is controllable in a non-uniform manner on a frame-to-frame basis. For example, the number of actual channels may vary, and certain ones or all of them may be outputting silence.
General background to the invention is given by the following earlier documents, all being at least co-assigned to the present assignee and being herein incorporated by reference:
EP Patent 402 973, EP Patent Application 660 540, corresponding U.S. Pat. No. 5,323,396, issued Jun. 21, 1994, which is a continuation of U.S. application Ser. No. 07/532,462, abandoned; U.S. Pat. No. 5,606,618, issued Feb. 25, 1997; U.S. Pat. No. 5,530,655, issued Jun. 25, 1996; U.S. Pat. No. 5,539,829, issued Jul. 23, 1996; U.S. Pat. No. 5,777,992, issued Jul. 7, 1998; and pending U.S. application Ser. No. 08/488,536, describing a Musicam Layer 1 encoder and decoder for L and R signals;
EP 678 226, corresponding to U.S. Pat. No. 5,544,247, issued Aug. 6, 1996, describing encoding and decoding of L, R and C channels;
U.S. patent application Ser. Nos. 08/032,915, 08/180,004, 08/427,046, describing the matrixing of bitrate-reduced L, R, C, SL and SR signals.
Now, in a consumer application (SPDIF) of the above specified digital video disc, two subframes are specified that each can simultaneously carry 32 bit data words. This allows to transfer via the IEC 958 bitstream either 2-channel linear PCM audio, or a set of alternating bitstreams, but not those configurations simultaneously. The IEC 958 standard specifies a widely used method for interconnecting digital audio equipment with 2-channel linear PCM audio. A need has been encountered to allow transferring non-PcM encoded audio bitstreams for consumer applications in the same protocolled environment, and in particular pause bursts, in case one or more of the audio channels would represent silence. In particular, the granularity of such pause representation at the receiver side should be sufficiently brief from a perceptive standpoint.